1. Field of the Invention
This invention relates to an opening/closing apparatus which prevents abrupt fall and rotation of a keyboard cover in a keyboard musical instrument.
2. Description of the Prior Art
Japanese Patent Laid-Open No. 41898/1988 proposes an apparatus having a construction wherein a coil spring is wound on a damper shaft supported rotatably inside a cylindrical case, a rotary damper is buried on both side surfaces at the rear end portion of the keyboard cover with one of its ends anchored to a recess of a cover portion of the case, a receiving metal is fitted to the inner surface of each crossarm or side plate of a musical instrument main body and the projecting end of the damper shaft is meshed with a U-shaped groove of the receiving metal so that when the keyboard cover is rotated by a predetermined angle in a closing direction, the spring fastens the damper shaft in order to thereby generate resistance and to mitigate drop impact.
However, since the damper member of the apparatus described above winds the coil spring on the damper shaft and stores it in the case which permits contraction and extension of the spring, it has a relatively large capacity but the keyboard cover is structurally limited so as not to impart any trouble in the appearance of the instrument, in the playing operation, in the fitting/removing operation, and so forth. Therefore, even when the damper member described above is fitted to the thick base end portion, its fitting position is naturally limited. Since the support member of the damper case projects to the inner surface of the cover, flatness of the cover is lost. Furthermore, since the keyboard is supported by meshing the damper shaft with the U-shaped grooves of the receiving metals on the musical instrument main body side, the weight of the keyboard cover is always borne by the damper shaft and excessive force is applied to the damper shaft. Since the damper is of a spring type, there is the drawback that the keyboard cover tends to somewhat float under the finally closed state due to repulsive force of the spring.